The present invention relates to a cathode ray tube provided with a potted base and, more particularly, to an improvement in the potted base.
A cathode ray tube is frequently used as a transmission means of instructions and/or information in control devices for various types of equipment and systems. These control devices are quite frequently used under extremely severe conditions. Moreover, high reliability is required for the control devices including display devices since troubles of the display devices may lead to serious accidents of the overall systems under the control of the control devices. An example of such a control device is a pilotage control section of an aircraft.
In a cathode ray tube for a general television receiver, connecting leads from a drive circuit are connected through a socket to stem pins extending from the base of the cathode ray tube. If such a cathode ray tube is used for the control devices of the type as described above, the reliability is significantly degraded due to creeping discharge caused by high humidity or a drop in the atmospheric pressure, incomplete contact between the socket and stem pins caused by vibrations, and degradation in the mechanical strength.
For this reason, in a cathode ray tube for a control device of the type described above, connecting leads from a drive section are connected to the stem pins, and the overall base is sealed and insulated with an insulating adhesive such as silicone rubber.
An example of a cathode ray tube of this type will now be described with reference to FIGS. 1 and 2. Referring to these figures, the cathode ray tube comprises a panel or faceplate 2 with a phosphor screen 1 formed on its inner surface, a neck 4 connected to the panel 2 through a funnel 3, a stem 7 through which extend stem pins 6 which support an electron gun 5 mounted within the neck 4 and which apply a predetermined voltage to the respective electrodes of the electron gun 5, and a base 8 connected to the outer side of the stem 7. In order to connect the stem pins 6 to the drive circuit, the base 8 is tightly adhered to the outer side of the stem 7 with an insulating adhesive 9, as shown in FIG. 2. Then, a plurality of connecting leads 10 from the drive section are connected to the stem pins 6 through terminals 11. A mold 12 of a silicone resin is mounted such that its axis is aligned with the axis of the tube, and a sealing material 13 is applied to seal a gap between the mold 12 and the neck 4.
Silicone rubber 14 defoamed under a vacuum is injected into the mold 12 and cured. Thereafter, the sealing material 13 and the mold 12 are removed.
In this manner, the leads 10 are connected to the stem pins 6, and are sealed and insulated by the silicone rubber 14.
A cathode ray tube of this type requires a jig so as to mount the axis of the mold 12 substantially in alignment with the axis of the tube. Care must be taken to completely seal the silicone rubber 14. Although the silicone rubber 14 is defoamed under a vacuum before injection, air may be trapped therein during injection. If the injection speed of the silicone rubber 14 is increased, an air void is formed inside the mold 12, thus degrading insulation characteristics.